Liquid-based Solid Imaging, for example, stereolithography, is a process whereby a photoformable liquid is applied as a thin layer to a surface and exposed to actinic radiation such that the liquid solidifies. Subsequently, new thin layers of photoformable liquids are coated onto previous layers of liquid or previously solidified sections. The new layers are then exposed imagewise in order to solidify portions imagewise and in order to induce adhesion between portions of the new hardened region and portions of the previously hardened region. Each imagewise exposure is of a shape that relates to a pertinent cross-section of a photohardened object such that when all the layers have been coated and all the exposures have been completed, an integral photohardened object can be removed from the surrounding liquid composition.
Three-dimensional articles produced from conventional hybrid compositions (a composition with both cationically curable and free radical curable compounds) by stereolithography tend to have low clarity. In particular, such articles may be hazy and/or highly colored. This haziness is likely due in part to poor miscibility of the cationically curable and free radically curable compounds, which is accentuated by their different rates of reaction.
U.S. Pat. No. 6,811,937 discloses a radiation curable hybrid composition which produces three-dimensional articles having improved clarity. The hybrid composition contains a cycloaliphatic epoxy and low molecular weight polyTHF combined with specific acrylates, in particular, erythritol hexacrylate. WO05045523 also discloses a photocurable hybrid composition for producing high clarity three-dimensional articles in which the epoxy component contains little or no glycidyl epoxy compound.
An object of the present invention is to provide an improved photocurable hybrid composition having higher carbon and hydrogen content and low or no antimony content that, upon cure, produces a three-dimensional article that is clear, colorless, and also maintains excellent mechanical properties, including high strength and water resistance, for longer periods of time which can be used in various applications.